Lead ring removal from a steam still

ABSTRACT

Lead ring deposits formed by the deposition of solid lead particles on steam still surfaces are removed by directing a fluid such as water, maintained at high pressure across an orifice at the surface to be cleaned. Pressures of 2,000 to 10,000 p.s.i.g. are employed across the orifice plate from which the fluid is directed against the surfaces to dislodge or explode the adherent lead ring from the still surfaces quickly and efficiently thereby eliminating the tedious mechanical scraping methods previously employed.

D United States Patent 1151 3,661,643

Lytton et al. [4 1 May 9, 1972 [541 LEAD RING REMOVAL FROM A 1,603,541 10/1926 Huff ..134/22 STEAM STILL 1,827,085 10/1931 Huff ..134/8 2,326,525 8/1943 Diwoky... ....134/8 X [721 lnvemrs= 14m, Sllsbee; 2 626 879 1/1953 Lazar ..134/22 x bmh 3,104,989 9/1963 Sedgwick et a1 ..134 8 [73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

Primary E.\aminerMorris O. Wolk [22] Filed 1971 Assistant Examiner-Joseph T. Zatarga [2]] Appl. No.: 129,441 AttorneyChisholm & Spencer Related U.S. Application Data 57] ABSTRACT [63] continuationin'pan of 51320 Jan 1970 Lead ring deposits formed by the deposition of solid lead parabandonedticles on steam still surfaces are removed by directing a fluid such as water, maintained at high pressure across an orifice at U.S. Cl ..l34/34, 134/17, 134/22 the Surface to be Cleaned Pressures of 2,000 to 10,000 are employed across the orifice plate from which the fluid is [58] Field ofSearch ..134/34, 7, 8, 22,17 directed against the surfaces to dislodge or explode the herent lead ring from the still surfaces quickly and efficiently [56] References Cited thereby eliminating the tedious mechanical scraping methods UNITED STATES PATENTS prevlously employed- 1,578,053 3/1926 McAfee ..134/22 10 Claims, 3 Drawing Figures Patented May 9, 1972 3,661,643

FIG. 2

FIG. 3

FIG. 1

INVENTORS lRW/V V. AYTTOIV 64/54 7: 066.65

BY W

ORNEYJ LEAD RING REMOVAL FROM A STEAM STILL CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part application of U.S. Pat. Ser. No. 5,320, filed Jan. 23,1970, now abandoned.

BACKGROUND OF THE INVENTION In the manufacture of tetraalkyllead compounds such as tetraethyllead and tetramethyllead it has been conventional practice to recover the tetraalkyllead product from a steam still. Typically this recovery of tetraalkyllead compounds from steam stills involves steam distilling tetralkyllead from a water mixture of the tetraalkyllead and solid lead particles suspended in the water. These water mixtures typically are agitated in a vessel which also contains anti-agglomerants to minimize any balling up of the solid lead particles during agitation of the liquid in the still. Typical of the anti-agglomerants employed are sodium thiosulfate and sodium dichromate. The use of such compounds and the steam distillation systems in a tetraalkyllead manufacturing process typically employed are generally described in U.S. Pat. Nos. 2,777,867; 2,004,160; 2,513,654 and 2,513,659.

Despite all the efforts made to prevent agglomeration of the suspended solid lead particles encountered in these tetraalkyllead recovery stills during steam distillation, it has been found that after a period of operation in a typical agitated still vessel lead deposition on the walls and the bottom of the still does indeed occur. Eventually the deposition of this solid deposit of lead builds up to a considerable depth on the vessel surface and results in binding of the agitation blades. When this occurs the still is taken out of service for cleaning. This cleaning of lead deposits on the still surfaces, commonly called lead ring" in the art, typically involves the use of long handled chisels and like devices which are used to scrape the deposited lead from the vessel wall. As will be appreciated this procedure is tedious, prolonged and results in considerable lost production time for the still undergoing a cleanup for lead ring deposition.

THE PRESENT INVENTION In accordance with the present invention a method of removing lead deposits from a steam still surface is provided which effectively and rapidly removes such a lead ring deposit. Thus, in accordance with this invention a portion'of the surface of the steam still covered by the deposit is typically exposed and then subjected to the action of a fluid stream maintained at an extremely high pressure behind an orifice so that it strikes the surface it is directed against at high velocity to thereby dislodge or explode the lead particles adjacent the exposed area from the surface. This application of high velocity fluid streams is continued against fresh surface as it is exposed by the dislodging of lead from the still surface until the still surface is preferably free from any appreciable quantities of lead.

In practicing the instant invention fluid pressures of between about 2,000 to about 10,000 p.s.i.g. are typically employ'ed across the orifices in the fluid containing conduits. Thus, the fluid directed against the surface to be cleaned is directed at these surfaces across an orifice at pressures of this magnitude. The fluid used is preferably water but any safe, economical fluid capable of being fed at these pressures can be used such as trichloroethylene, perchloroethylene, mineral acid solution, or suspensions of sand and other solids in water. The velocity of the fluid striking the still surfaces across orifices at the above stated pressures is typically 400 to 1,300 feet per second.

In exposing the surface of the still to the action of high pressure fluid recourse may be had to any of several alternatives without departing from the spirit of the invention. Thus if desired, one or several target sites can be exposed by chiseling lead from the still surface in one or more places. In the preferred operation the initial exposure of the still surface below the lead deposit is accomplished by directing the high pressure fluid against a designated area of the still surface for a period of time sufficient to wear away the lead thereon and expose the base material. The base in these stills is typically metal such as steel but the invention may be practiced with equal facility using other surfaces such as ceramic surfaces.

In the preferred operation of the instant invention the high pressure fluid is spaced from the vessel wall a fixed distance. This is typically between one-fourth to 12 inches from the surface of the vessel, preferably between 1 to 6 inches. A particularly advantageous method of accomplishing this application of fluid uniformly over the vessel surfaces having lead deposited thereon is to provide a nozzle member which is inset in a circumferential collar a distance of one-fourth to threefourths of an inch. The collar can then be placed against the heavy lead ring deposit and by moving the collar over the surface, equal spacing of the fluid from the surface is readily real-' ized.

For a more complete and detailed explanation of the instant invention reference is made to the accompanying drawing in which:

FIG. 1 is a side elevation of a steam still with one wall broken away to show the internals;

FIG. 2 is a cross section of FIG. 1 taken along lines 11-11 to show the blade configuration on the agitator; and

FIG. 3 is a cross section of the nozzle member 9 of FIG. 1.

Turning to the drawing and FIGS. 1 and 2 in particular there is shown lead rings or deposits 27a and 27b on the bottom and sides of a steam still 10 used in the manufacture of tetraalkyllead. The deposits are shown as the two types typically found in steam stills from which tetraalkyllead is recovered. Deposit 27a is a relatively dense, hard deposit and is usually the type of lead deposit or ring found under the agitator blades of the vessel. The deposit 27b is less dense than deposit 27a and is in general relatively thick, but soft. This deposit 27b is located usually above and to the outside of the agitator blades.

The still 10 is provided with a cover 20. On the cover 20 two openings 21 and 22 are provided. Opening or access port 21 during operation of the vessel as a steam still is used as a product vapor outlet and is usually connected to a suitable vapor line under this condition. Opening 21 is also used to insert lance member 11 when the method of the instant invention is employed. The opening 21 is shown being used to practice invention in FIG. 1.

A motor 19 is mounted on cover 20 of still 10 and is attached to a shaft 24. Shaft 24 has a plurality of blades l3, l4, l5, l6, l7 and 18 mounted at the bottom thereof. Motor 19 when operating rotates the shaft 24 which in turn rotates the blades 13, 14, 15, 16, 17 and 18. Still 10 is provided with a discharge valve 23 on the bottom thereof.

Turning to FIG. 1, the lance 11 is shown inserted into the interior of vessel 10 through access port or opening 2l. ln the drawing the lance 11 is shown positioned above the deposit 27a and connected at its upper end to hose 6. It will of course be understood that lance 11 while shown in the drawing above deposit 27a, can be easily moved around inside vessel 10 so that fluid jetting from nozzle 9 on the end of lance 11 can be directed against lead ring in the vessel 10 wherever it is located.

The nozzle member 9 as shown in FIG. 3 is attached to the lance with threads 8 and is provided with an orifice 7. Orifice 7 is recessed and is protected by a collar member 8 circumferentially disposed around the orifice 7. This collar 8 prevents the orifice from becoming damaged or plugged by contact with the wall of vessel 10 and also spaces the orifice 7 a fixed distance from the surface of lead ring 270 when the collar is placed against the surface thereof.

The lead rings 27a and 27b located on the surfaces of still 10 have the appearance of solid metal coating but are porous in nature. Thus, as the high pressure fluid is directed against the surface of ring 27a for example, it is theorized that the fluid quickly finds its way through the pores of ring 27a to the solid surfaces underneath, is deflected from that solid surface and lifts the coating adjacent that surface away from it. Whatever the mechanism however, ithas been found that by applying the fluid pressure to these lead rings 27a and 27b as described hereinafter, the rings 27a and 27b are quickly and efficiently removed and the lead ring cleaning operation is found to require 600 to 800 per cent less time than the prior mechanical methods of removal;

As can be seen from the drawing the lead ring buildup on a steam still varies in thickness and consistency depending upon its location in the still vessel. Thus, a relatively thin, dense deposit 27a is typically found at the bottom of these vessels and relatively thick but softer deposits 27b are found adhering to the walls of the still vessels. The hardest deposits are usually those under the blades of the agitator at the bottom of the still.

In a typical operation designed to remove lead ring deposits from a steam still such as shown in FIG. 1, the lance 11 is first placed above the soft deposit 27!: beginning with the uppermost buildup shown. Water is admitted through hose 6, lance I1 and nozzle 9 via the orifice 7 and directed against the deposit 27b until it is removed from the walls of still 10. Since this deposit is relatively soft, despite its thickness, it is usually found that the lance can be rotated around the vessel rapidly while directing the fluid against these deposits and they are removed very quickly. The thick deposit 27a positioned at the bottom of the vessel may be successfully removed by directing the water or other fluid from orifice 7 against a site or location on that deposit for a period of time sufficient to expose the metal surface beneath that state. Once the metal is exposed the fluid is continued to be directed againstthe surface and the adjacent lead. It is found that the lead deposit despite its thickness and density is exploded or dislodged from the still surface quite readily. This procedure is continued until the thick deposit 27a is essentially completely removed.

A typical application of the instant invention to a lead fouled still will now be described with reference to FIG. 1.

EXAMPLE A steam still 10 about 7 feet in diameter and about l2 feet in height overall was covered with a lead ring deposit of varying thickness. The deposit ranged generally between 4 to 10 inches at the bottom of the vessel to 4 to inches or more, along the sides of the vessel immediately adjacent and above the agitator Made. A lance 11 about 14 feet long and equipped with a nozzle member 9 was inserted into the still through sn access manhole 21. The nozzle member 9 was spaced about 4 inches from the surface of the upper deposit 27b and water was directed against the upper side of the deposit 27b at a pressure across the orifice 7 of 6,000 p.s.i.g. The water velocity at this pressure was 800 feet per second. The lance 11 was rotated in circular fashion around the wall of the still 10 with the water constantly being directed against the upper edge of deposit 27b and the wall of still 10. The deposit 2711 was found to fall away rapidly upon contact with the high pressure water. After the deposit 27b on the side of the still 10 was essentially completely removed, high pressure water was then directed against the deposit 270. In this instance lance l1 and nozzle 9 rested against the deposit 27a. This contact was continued until the surface of the still was exposed beneath this deposit. The water was then continuously directed against the surface of the still 10 at the 6,000 p.s.i.g. orifice pressure and the lead adjacent the exposed still surface as it was being exposed. This caused the lead deposit 27a to explode or violently dislodge from the still surface. In general the orifice 7 was typically one-fourth of an inch above the surface of deposit 27a against which the water was directed in this operation at the bottom of the still.

The entire operation which resulted in the removal of 95 per cent or more of the lead present on the vessel wall at the start took a period of about one-half hour. In a normal mechanical cleaning operation of a similarly lead fouled still it was estimated that a cleaning time of 6 to 8 hours would be retwired. I

hile the invention has been described with reference to certain specific embodiments, it is not intended that it be limited thereto except insofar as appears in the accompanying claims.

We claim:

1. A method of removing a lead deposit formed on the surface of a steam still from which tetraalkyllead is recovered from an aqueous mixture of tetraalkyllead and metallic lead, comprising exposing a portion of said surface, contacting said exposed surface with a fluid stream directed against the surface at high velocity from an orifice which maintains the fluid at high pressure behind the orifice to thereby dislodge lead adjacent said exposed surface, and continuing the application of said high velocity fluid to fresh surface as it is exposed until a substantial quantity of said lead deposit is removed.

2. A method of removing a lead deposit formed on the sides and bottom of a steam still, said deposit being caused by the deposition of solid lead particles thereon from an aqueous mixture of tetraalkyllead and solid lead subjected to steam distillation and agitation, comprising exposing a surface of the still under the lead deposit by directing fluid maintained at high pressure behind an orifice against a target area on said opposite for a period of time sufficient to cause the lead to be worn away to the surface of the still, continuing to direct the said high pressure fluid stream against the exposed surface to thereby dislodge the lead adjacent thereto and expose fresh surface and continuing the application of the high pressure fluid against freshly exposed surfaceuntil a substantial portion of the lead deposit is removed.

3. The process of claim 1 where the fluid stream is maintained at pressure of 2,000 to 10,000 p.s.i.g.

4. The process of claim 2 wherein the fluid stream is maintained at pressure of 2,000 to 10,000 p.s.i.g.

5. The process of claim 1 wherein the fluid stream is maintained at pressure of 6,000 p.s.i.g.

6. A method of removing lead ring from a stream still in which tetraalkylleadis recovered by steam distillation from an aqueous mass of tetraalkyllead and solid lead particles and wherein the solid lead deposits on the still surfaces to form a solid adherent lead containing deposit thereon the steps comprising spacing a high pressure nozzle a fixed distance from the lead surface, projecting a fluid through the nozzle and against the lead surface at high velocity for a period of time sufficient to wear the lead away and expose the still surface, continuing to direct the fluid at high velocity against the still surface and adjacent lead to discharge the lead and expose fresh still surface and continuing this application of high velocity fluid against fresh still surface as it is exposed until the lead is substantially removed from the still surface.

7. A method of removing lead ring from a steam still in which tetraalkyllead is recovered by steam distillation from an aqueous mass of tetraalkyllead and solid lead and wherein lead deposits on the still surfaces form a solid, adherent deposit thereon, the steps comprising placing a conduit having a high pressure nozzle at the end thereof a short butspaced distance from the surface of the lead ring, contacting the lead surface with a fluid directed across the high pressure nozzle to thereby dislodge the lead deposit.

8. The method of claim 6 wherein the velocity of the fluid is between about 400 to about 1,300 feet per second.

9. The method of claim 7 wherein the high pressure fluid is introduced against the surface from a distance of about onefourth to 12 inches.

10. The method of claim 7 wherein the high pressure nozzle maintains the fluid at pressure of 2,000 to 10,000 p.s.i.g.

ra sa a 

2. A method of removing a lead deposit formed on the sides and bottom of a steam still, said deposit being caused by the deposition of solid lead particles thereon from an aqueous mixture of tetraalkyllead and solid lead subjected to steam distillation and agitation, comprising exposing a surface of the still under the lead deposit by directing fluid maintained at high pressure behind an orifice against a target area on said opposite for a period of time sufficient to cause the lead to be worn away to the surface of the still, continuing to direct the said high pressure fluid stream against the exposed surface to thereby dislodge the lead adjacent thereto and expose fresh surface and continuing the application of the high pressure fluid against freshly exposed surface until a substantial portion of the lead deposit is removed.
 3. The process of claim 1 where the fluid stream is maintained at pressure of 2,000 to 10,000 p.s.i.g.
 4. The process of claim 2 wherein the fluid stream is maintained at pressure of 2,000 to 10,000 p.s.i.g.
 5. The process of claim 1 wherein the fluid stream is maintained at pressure of 6,000 p.s.i.g.
 6. A method of removing lead ring from a stream still in which tetraalkyllead is recovered by steam distillation from an aqueous mass of tetraalkyllead and solid lead particles and wherein the solid lead deposits on the still surfaces to form a solid adherent lead containing deposit thereon the steps comprising spacing a high pressure nozzle a fixed distance from the lead surface, projecting a fluid through the nozzle and against the lead surface at high velocity for a period of time sufficient to wear the lead away and expose the still surface, continuing to direct the fluid at high velocity against the still surface and adjacent lead to discharge the lead and expose fresh still surface and continuing this application of high velocity fluid against fresh still surface as it is exposed until the lead is substantially removed from the still surface.
 7. A method of removing lead ring from a steam still in which tetraalkyllead is recovered by steam distillation from an aqueous mass of tetraalkyllead and solid lead and wherein lead deposits on the still surfaces form a solid, adherent deposit thereon, the steps comprising placing a conduit having a high pressure nozzle at the end thereof a short but spaced distance from the surface of the lead ring, contacting the lead surface with a fluid directed across the high pressure nozzle to thereby dislodge the lead deposit.
 8. The method of claim 6 wherein the velocity of the fluid is between about 400 to about 1,300 feet per second.
 9. The method of claim 7 wherein the high pressure fluid is introduced against the surface from a distance of about one-fourth to 12 inches.
 10. The method of claim 7 wherein the high pressure nozzle maintains the fluid at pressure of 2,000 to 10,000 p.s.i.g. 